---
lang: en
title: 'API docs: authentication.authenticatefn'
keywords: LoopBack 4.0, LoopBack 4, Node.js, TypeScript, OpenAPI
sidebar: lb4_sidebar
editurl: https://github.com/loopbackio/loopback-next/tree/master/packages/authentication
permalink: /doc/en/lb4/apidocs.authentication.authenticatefn.html
---

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[Home](./index.md) &gt; [@loopback/authentication](./authentication.md) &gt; [AuthenticateFn](./authentication.authenticatefn.md)

## AuthenticateFn interface

interface definition of a function which accepts a request and returns an authenticated user

**Signature:**

```typescript
export interface AuthenticateFn 
```